MICROBES IN THE HUMAN BODY 29 



of plants under sterile conditions and their rational culture 

 with the help of selected microbes. Pasteur expressed an 

 opinion which he had not time to submit to experiment, but 

 which has been taken up by others, the idea namely that an 

 animal cannot dispense with the bacteria' living within it. He 

 suggested that a young animal should be fed from birth with 

 pure sterile food. 



" I do not conceal the fact that, had I time to undertake 

 this study, I should do so with the preconceived opinion that 

 life under such conditions would become impossible. Given 

 that such experiments are capable of being gradually simplified, 

 it might be possible to study digestion by adding systematically 

 to the sterile food of which I speak various individual bacteria 

 or different bacteria together, each of definitely known species. 



"The hen's 'egg lends itself without serious difficulty to 

 experiments of this kind. Previously freed externally from 

 every sort of living impurity just before hatching, the chick 

 should be immediately put into a chamber free from every 

 sort of bacterium, so that it could be supplied with pure air 

 and with sterile food, easily introduced from without in the 

 shape of water, milk, and corn. 



"Whether the result were positive, confirming the precon- 

 ceived idea which I am putting forward, or negative, or even 

 absolutely the opposite, i.e., that life without bacteria is easier 

 ajid more vigorous, in any case the experiment would be full 

 of interest." 



The experiment has been tried and the programme is still a 

 long way short of completion. One thing only has to be 

 altered in Pasteur's statement. The experiments are far from 

 being without " serious difficulty.'' 



Two currents of opinion have developed. The first, following 

 literally Pasteur's idea, maintains that animals are like plants 

 and cannot nourish themselves with the sole help of their own 

 digestive juices but require also the intestinal microbes. We 

 do not know, say its supporters, if in the beginning of life an 

 animal organism has ever developed free from micro-organisms ; 

 it is not very probable ; what is certain is that for centuries and 



